Has Tesla Considered a "Dedicated Regen" battery?

[LMichel]

How about a limited battery that occupies the frunk and is based on a chemistry unlike the main battery?

Prior to owning a MS, I owned a Chevy Volt for 4 years. That car would regen regardless of the temperature. Of course the car would quietly charge only to about 80% and then report full, so any regen at the start of a topped-off trip would have 'somewhere to go'.
But, even with zero degree weather, the battery would still take the regen charge.

I started thinking;
Why not have a separate battery - with chemistry similar to the Chevy Volt battery? Locate that battery in the frunk. It's primary function is to take ALL regen and then meter its energy out to the main battery.
This way, regen functionality would be consistent, regardless of temperature conditions?

I would guess that a 5kW battery would be more then enough. My Volt had a 10kW battery as it's only battery and would give me almost 50 miles. Judging that it was 'secretly' charged to 80% max, that leaves roughly 2kW of reserve storage on the top end. Since regen never filled it, I have to deduce that I never put in more than 2kW of regen. So 5kw seems very reasonable. If weight, were an issue, even a 3kW battery would work?

Okay, I'm ready for your "hole poking"

 

[Rocky_H]

Well, first hole to poke in this is that you've been using kW throughout that whole post, when you should actually be using kWh, since you are talking about energy, not power.
So now, I guess there are just some minor things: The first is just does it seem worth it? You give up extra space for battery that is smaller and therefore isn't part of the main battery and therefore can't be charged at the same high rate as part of the really large main battery (C rate) when Supercharging.

Secondly, I think you may be making some assumptions that what the Chevy Volt does is not harmful to the battery. I don't know if there is any type of lithium ion battery chemistry that can charge when it's really cold without causing that plating effect, which degrades the life and capacity of the battery. Chevy may just do it anyway, despite the damage, for a few reasons: (1) I don't think they have temperature management of the pack, so they won't have that process like Tesla does, where it warms up the battery so it can do more regen in a little bit. So their option would be no regen at all through the winter to protect the pack, or just let it happen. (2) As you have pointed out, they do not use the full capacity of the battery, so a little bit of damage and loss of capacity can just be taken out of the unused portion without being very noticeable to the car's use.

One of the possibly more useful ideas I like and I've seen other people mention is to have the relay circuitry in the car so that when slowing, the regen current from the motor would directly drive the battery pack heater. That battery pack heater runs up to 6kW of power. So that would be some resistive load on the motor, providing a little bit of slowing force, and you have the added bonus that some of the battery heating energy would be recovered kinetic energy (less waste) instead of drawing all of it out of the battery's stored energy.

 

[NeverFollow]

Hi, I'm not sure to understand how you plan to capture the re-gen energy and how to send it back to the main battery.
Dealing with 400 Volts, is not an easy task. But I would be interested to know a little bit of more about your project.

However, I was thinking about that having a second 12 Volts battery could be useful for some people.

Tesla doesn't provide any way to get power, for example power your house using your car in case of power outage, like other EV do.

The only power available is a 12 Volts outlet cigaret adaptor or taping the OBD 2, but you cannot get too much power from those,
and you might have to turn the camper mode to keep the power on.

Some people would like to get access to some source of energy, for example to power a small fridge,
run or re-charge some power tools if you are a contractor working a house not yet connected to the grid,
use a power inverter to run some computers...

There are some integrated portable power stations combining a battery and an inverter.

I was thinking then to have an automatic charging relay to charge the second 12 Volts battery from the first battery
when needed, but isolating the two batteries otherwise. This is commonly used in boats or RV.

This system would provide a constant power source of energy while keeping the system isolated from the main 12 Volts battery,
except from a 12 Volts cable connected to the 12 Volts outlet cigaret adaptor and isolated using a charging relay.
So the Tesla warranty would not be affected, as everything could be easily removed.

 

[Rocky_H]

Tesla doesn't provide any way to get power, for example power your house using your car in case of power outage, like other EV do.

Other than the Leaf having the vehicle to home in Japan only, can you name any other EVs that have this?

 

[SSedan]

The limited regen is a pretty brief issue, you are suggesting a hugely complicated and expensive addition to try and mitigate a minor hassle.

Also in order for the pack to absorb that energy it would have to be fairly large, the smaller the faster it will heat up, so it is not like you could have a little 10kwh pack and regardless of chemistry expect to smack it with all that power.

Sort of like all the people who expect the MegaCharger to be rolled out for cars, as is when supercharging in warm weather the AC runs hard to cool the battery, How can they expect to push a crap load more power in faster?

I really wish Tesla could push an update to the cars and chargers and shorten my supercharger stops, but if the AC already runs hard to keep the battery cool enough in summer how much room for improvement is left?????

 

[LMichel]

Hmmm... All good thoughts.
However, the Volt *does* have battery temperature management. It will warm itself off the charger when plugged in. My 2013 Volt used 1.2kW when warming. This would only be active for about 5 minutes every two hours and when the temp was below freezing. I know this for a fact, because my charger is connected through an Amp meter - which is in turn connected to the solar array.
When the Volt is not plugged in (interestingly), the warming cycle still seems to happen, because the number of miles available will drop by about 2 or 3 for an entire 24hrs below freezing. My calculator says that about 0.5kWh were consumed from the battery when this happened. There was no concern that leaving the car in freezing weather (say at the airport) for weeks on end would drain the car, since there was an onboard ICE as a backup.

The Volt battery is something like 330V - if I remember correctly. It's also roughly about 14" X 60" X 8" for 10kWh... Yes, I did mistake kW for kWh in my original post... Good catch
So cutting that battery into a third (14" X 20" X 8") would make it pretty easy fit for the frunk. Now there is 3.3kWh of silo regen capacity.
The supercharger (and any charger) would never charge the regen battery. ONLY regen charges the regen battery. Current from that battery only travels from the motors to the battery on regen, and from the battery to the main Tesla battery (when conditions are right for it to accept energy).

I live in the Northeast. Lack of regen is NOT a minor inconvenience. I can drive my MS (range mode or not) for 45 minutes and still not have regen! To me, this is dangerous since I now have two 'driving profiles' to consider when taking my car out to go somewhere in the winter. Not only that, but I sort of have to be mindful of the car switching over to regen and adapt accordingly as it warms up.
California Tesla engineers should drive around Rochester, Buffalo or Syracuse NY for a full winter. Bet you a Roadster that they would then make some changes

Using 'wasted' regen available energy to temporarily warm the battery heater is another good idea. Hell, why didn't Tesla even just put some type of dump-load device in place?? It's wasteful, but at least regen would act consistently...

Don't get me wrong, my MS beats my Volt by a mile in terms of innovation. But, that regen thing just bugs the sh!t out of me

 

[SSedan]

Set the regen to low so you don't see such big swings in its performance.

What I was saying is you can't put that much regen into a smaller battery.

Why do you think you can cut the battery to a third then not cut the regen as well? Isn't it reasonable to presume the regen would be cut to a third as well?

I live near Green Bay colder averages here though I haven't been thru a winter yet I have seen what 9f does to regen and during the day my car is in an open windswept area so any charging/driving heat is gone by lunch if I leave.

I believe they were also sued for Regen causing rear tire slippage in icy weather so another reason to limit regen, in winter there can be ice patches at any time from melting snowbanks even if there hasn't been precipitation.

 

[jerry33]

I believe they were also sued for Regen causing rear tire slippage in icy weather so another reason to limit regen, in winter there can be ice patches at any time from melting snowbanks even if there hasn't been precipitation.

Use real winter tires and some common sense while driving and it's not a problem. Of course, people will sue for anything these days, so that's not any kind of issue either.

 

[iwannam3]

Don't you need to use the friction brake system occasionally to sweep rust off the rotors and keep the calipers free and working? I remember someone had an $8.000 brake bill in the northeast due to salt and infrequent use of the brakes?

 

[jerry33]

Don't you need to use the friction brake system occasionally to sweep rust off the rotors and keep the calipers free and working? I remember someone had an $8.000 brake bill in the northeast due to salt and infrequent use of the brakes?

Yes, that's why the regen doesn't go all the way down to zero.

 

[SSedan]

Use real winter tires and some common sense while driving and it's not a problem. Of course, people will sue for anything these days, so that's not any kind of issue either.

I am a competent driver accustomed to RWD in winter but let's face it most folks aren't. Given regen reduction begins around 50F it would seem it has a LOT more to do with taking care of the battery than tire slippage but a big company selling to hundreds of thousands of cars that have decidedly different characteristics than most other cars and limiting exposure for even frivolous lawsuits is a legitimate concern.

 

[Rocky_H]

I can drive my MS (range mode or not) for 45 minutes and still not have regen!

Uh, I think I'm going to have to call B.S. on that. Maybe you're referring to not having the full level of regen, which yes, that's for sure going to be the case.

California Tesla engineers should drive around Rochester, Buffalo or Syracuse NY for a full winter. Bet you a Roadster that they would then make some changes

Right...instead of Norway, where they do their cold weather testing.

 

[LMichel]

Uh, I think I'm going to have to call B.S. on that. Maybe you're referring to not having the full level of regen, which yes, that's for sure going to be the case.

Duly Noted:
Yes, 45min before I have FULL regen. But at least 15 before I have any regen at all.
I would settle for ...maybe 5 minutes!

Right...instead of Norway, where they do their cold weather testing.

Testing is not driving for an entire winter.

 

[Big Earl]

Duly Noted:
Yes, 45min before I have FULL regen. But at least 15 before I have any regen at all.
I would settle for ...maybe 5 minutes!




Testing is not driving for an entire winter.

Do you ever preheat the car before driving? If so, does it help with the cold weather regen situation?

 

[gavine]

Do you ever preheat the car before driving? If so, does it help with the cold weather regen situation?

Or schedule the overnight charging so that it finishes right-before it's time to leave. Charging, at least with a decent amount of current, warms the battery so doing this will enable regen and save energy.

 

[LMichel]

Today I preheated the car for 10min prior to departure. I also had it charge for an hour before leaving. This is with a 3500W level2 charger.
Outside air temp was 44 degrees.
I timed it with my phone: No movement/reduction in the regen arc for 22 minutes! At 41 minutes, the regen arc was gone.
At 55 minutes my trip was complete. So I had full regen for 14min of a 55min trip, and at 44F degrees.

 

[Big Earl]

Today I preheated the car for 10min prior to departure. I also had it charge for an hour before leaving. This is with a 3500W level2 charger.
Outside air temp was 44 degrees.
I timed it with my phone: No movement/reduction in the regen arc for 22 minutes! At 41 minutes, the regen arc was gone.
At 55 minutes my trip was complete. So I had full regen for 14min of a 55min trip, and at 44F degrees.

Was this with range mode on or off?

 

[Rocky_H]

I kind of feel that some people are getting into missing the forest for the trees, like seeing the regen limit line and just knowing that it is there is what's bothering them, even if they have 40kW out of a potential 60kW, and the driving feel isn't much different. I totally acknowledge, though, that when it's so cold that regen is totally gone, that is a pretty startling and uncomfortable feeling. Fortunately, that does usually ease off to start taking some regen within maybe 5-10 minutes-ish.

I know the complaint is that the feel is different, but from the other end of the telescope, it is going to consistently feel this way every cold morning throughout the winter, so is that really different? The missing regen does feel weird, but the partially limited is something you get used to easily. And that's why I do think it's a little obsessive trying to get rid of the partial limiting completely, versus it being valuable to reroute that energy somehow to simulate that partial limiting that you get frequently. The batteries like body temperature, and it's hard to keep the pack that warm all the time and would be quite a waste of energy.

 

[jerry33]

Today I preheated the car for 10min prior to departure. I also had it charge for an hour before leaving. This is with a 3500W level2 charger.
Outside air temp was 44 degrees.
I timed it with my phone: No movement/reduction in the regen arc for 22 minutes! At 41 minutes, the regen arc was gone.
At 55 minutes my trip was complete. So I had full regen for 14min of a 55min trip, and at 44F degrees.

This sounds as if you had range mode on during charging and heating. Range mode should be off when plugged in or there will be only minimal heat to the battery (probably close to zero at 44F).

 

[kiwiguy]

For regen, you don't want a separate battery, you want a super capacitor as it is way more efficient.
Use it to buffer out the peaks and lows of power draw from the battery.